iMac 27 inch 2020 - Screen Glitch (Random Lines Appear on Screen)

Try the following: download and apply the macOS Catalina 10.15.7 Combo Update   

It fixes this issue:

• Addresses a graphic issue that may occur on iMac (Retina 5K, 27-inch, 2020) with Radeon Pro 5700 XT

Apple does publish some acoustic benchmarks, for idle at least you can find the measured dB values at the bottom of each product spec:

https://support.apple.com/kb/SP821

https://support.apple.com/kb/SP790

I think I've seen somewhere on their website also a comparison of acoustic performance for peak CPU usage, but can't find it now.

Either way, by the raw numbers the iMac 2020 is supposed to be quieter than the iMac 2019, but my experience is the very opposite. The 2019 model I had was dead quiet when idle or when browsing in Safari. Whereas the 2020 model just hums here audibly while I'm writing this in Safari and have 4 more tabs open and nothing else running. Same low temperature, same RPM and same low CPU usage.

I've no scientific proof for this, but my theory is that the 2020 iMac is perceived as louder perhaps because of the "different shape of the sound". From iMac 2020 they've removed the mechanical drive thus left a lot of empty space in its place: https://youtu.be/GIHSyamWnh4?t=63. I think this might be causing some sort of echoing of the fan noise. For me personally the 2020 iMac sounds more "tinny", or as some other commenter said, more "coarse". The actual dB values might be same or lower, but the sound itself is more annoying to my ears lol.

And because of that, I decided to keep my i9 actually. I don't think the i7 would be any quieter in regards of ambient idle noise. And as for the peak CPU fan noise — I don't really care if it peaks 43dB a second or two later or earlier, it's loud anyway and I'll take the 10% gain in compiling time if it's available.

You should be able to find info specific to NZ (or whichever country anybody else is interested in) from here: https://www.apple.com/legal/warranty/statutoryrights.html

It’s how I discovered that being as though I’m in the UK, I’m covered against my Mac breaking down for SIX years! Meaning that Apple Care essentially just becomes accidental damage insurance

For those trying to reproduce the issue, in my case it behaves like this:

• regular occurrence every 30-40 minutes, without any special events executed
• if I watch YouTube in Safari it can occur more often
• if I watch QuickTime video it can occur more often
• if I’m on a (Slack) video call it can occur every 5 minutes

None of these are reproducible reliably though. Not sure what’s the exact trigger.

For those trying to get rid of the issue and wait until an official fix is out, on MacRumours it’s been confirmed that it doesn’t occur when:

• you change your screen resolution to something else from default (SwitchResX has good options)
• or when you connect a second display

my 2020 27" with 16GB has so many problems I dont know where to start. My old 2010 with just 1GB lasted 10 years without a single issue and was, imho faster than this POS.

1. will not wake up after monitor sleeps, crashes and recovers only after holding down the power button for 5 seconds
2. Memory hog on any video running in Safari causing a Safari crash and restart
3. Blue-tooth latency and automatic typing of empty spaces at 30 to 40 key presses that cannot be backspaced
4. Blue-tooth connectivity loss and recovered multiple times a day
5. Since the introduction of B.S. a straight forward recovery from a Time Machine backup is no longer possible, you have to do a clean install and manually re-install every piece of software using the immigration assistance.

I have downgraded to High Sierra on a brand new iMac to resolve a majority of issues but of course I cannot update my Adobe or Apple products beyond that version as well

Apple went two steps backwards on this device if you ask me.

Cinebench worked fine on my new 2020 27" iMac together with a few other benchmarks apps I tried (don't remember their names) - only when playing Civilization VI and only when in full screen the whole Mac OS system crashes on me.

I'm on my second iMac 27 inch 2020. The first one was shutting down intermittently an also had the glitch line appearing as well. I returned it it for an exchange which I received less than a week ago, and this one also has the glitch line that appears without warning. It flickers several times and then goes away and continues to happen. The still is from a video I capture with my phone while I was migrating while setting it up for the first time. This continues to happen to this day no matter what I am doing on the computer.

Indeed, that is currently what I have. Even if it's a soldered card, and you're definitely right with that some damage still might have occurred during shipping unfortunately. Although, it seems a lot of people are having issues... Kind of makes me think there might be something wrong with the soldering process itself, but I'm just speculating.

Take a screen shot & view that in Preview, move the Preview window around, if you see double lines it's a Video card/VRAM problem, if the lines do not move moving the pic around then it's the LCD or cable.

Same problem with my iMac 2020, already appeared during the initial Mac setup and keeps flashing randomly since then. Searching through YouTube and google it seems this is a common problem with the 5700XT gpu that comes with it.

I’m thoroughly disappointed, waiting for the customer service chat to come back online.

Same for me.

it started as soon as the first boot.

it’s not that frequent but does happen , even with no app opened.

i also get random crackles and distorsion on the built-in speakers, as well as loss of sync playing video. Only with the built-in speakers. But that’s for another thread.

Hi, I have experienced it the moment I finished the initial setups. I asked Apple Support and they told me to reset the SMC and NVRAM to solve the problem. It actually did for me, but I haven't started editing videos just yet, so it might not be stressful enough for the system to glitch again.

Have you received your replacement unit yet and has your issue been solved? I too get the line from time to time, but what is worse for me is the complete system crash looking like your screenshot, after playing Civilization VI through Steam for 10-15 minutes. I wonder if the issues are related.

Same issue with the white line here on macOS 10.15.6 with my AMD Radeon 5700XT 16GB Ram.

Not noticed it on Windows 10 yet.

SMC & NVRAM-Reset didn't help. Issue persists.

Also stressed the mac but it did not affect the issue. Seems to happen without any special impact.

Have one panic-shutdown-cause but I think this one was software-related.

Looking forward!

Greetings

Martin