Incoming background noise on Facetime and WhatsApp extremely loud but only with one person

My significant other and I have been long distance for about a year and a half. I have an iPhone 11 and a 6th Gen iPad; he has an Android phone and the same iPad. Since we've been apart, incoming calls from any combination of our devices on both Facetime and WhatsApp from him (and literally only him) amplifies his background noise to the point that I can't hear him. He insists that I'm the only person that he's ever had this problem with, and I've never had this problem with anyone else. The last time he visited, I demonstrated it for him by having FaceTiming him from his iPad and him answering me on my iPhone and he agreed that it was a horrible amount of noise. All of our devices are up to date and neither of us use headphones, AirPods, etc. for sound. Thoughts?