I have what sounds like the same problem as the original post: what sound like 'ticks' at irregular intervals and intermittent. It sounds like there is at least 1 other issue being described on this thread as well that has to do with a noisy or weak wi-fi connection.
I recorded the sound and it can be found here along with my notes: http://sprng.me/fenuv
I did some testing on the 'tick' issue and here's what I found:
Test tracks:
Stereophile test CD 3 test tone tracks 22 (1 kHz square wave), 23, 24
Equipment:
iPhone 4
Audioengine A2 powered speakers
Marantz SR5006
B&W Zeppelin Air
HTPC running Windows 7 and iTunes connected via Gb ethernet
Laptop running Windows Vista and Asset uPnP server connected via wi-fi 802.11g
Using Airplay:
- from iTunes on PC to Marantz SR5006 via Ethernet and AirPlay - tick sound (bad jitter?)
- from iPhone via home sharing and AirPlay to Marantz, iPhone line out, B&W zeppelin air: all had ticks
- from iPhone with track stored on iPhone to Marantz, B&W zeppelin air and AppleTV via AirPlay: had ticks,
- same track on iPhone via line out (to Audioengine A2's) did not have ticks
Using other input methods:
- when played using iTunes and PC analog out to Marantz (not airplay), no ticks heard
- when played via USB on Marantz, no ticks but slight warble sound (could be jitter but not as bad?)
- when played via DLNA (asset uPnP server on laptop via wifi), push from iPhone app and pull from receiver: no ticks, just like USB
- when played from CD on blu ray player connected via HDMI to Marantz: no ticks, just like USB.
Conclusions:
1. All AirPlay streaming has tick sound, including home sharing from iTunes on PC to iPhone, independent of AirPlay device manufacturer.
2. iPhone audio out does not have tick sound when playing file stored on iPhone.
3. Asset uPnP server playing via DLNA does not have tick sound even when playing from laptop connected via wifi.
4. CD and USB methods have no ticks and are same as USB.
The ticking and perhaps the slight warble sound I noticed during the USB, DLNA, and CD playback sounds like the jitter example track on Stereophile test CD 2. Can anyone confirm or disprove that this is jitter? Regardless it seems like AirPlay does not work as an audio streaming solution for critical listening.