Electrical buzzing when wireless charging on iPhone 12 Pro Max

I just bought the iPhone 12 Pro Max and use a third party wireless charger with it. I have noticed that once the iPhone is fully charged it starts making a very high pitched electrical buzzing or whining noise, fairly quietly but loud enough to wake me up in the middle of the night. I used the same charger with my previous iPhone XR and never experienced this issue so seems more likely to be an issue with the phone rather than the charger. Any advice would be greatly appreciated.