Loudspeaker hissing and "snow" noise

Repaired a customer’s S7 Edge screen and the loud speaker stopped working. Customer brought phone back when the new part came in and I noticed when it was dropped off that the loudspeaker was making a hissing noise and sounded like snow on a TV. After replacing loudspeaker, the problem did not go away. I had a spare S7 Edge at the shop (as all it does is bootloop), took the loud speaker out of it, and tried the 3rd speaker with customer’s phone- same problem.

Everywhere I look, the answer seems to be software/app related. I looked at the board, and compared it to other boards. No signs of a burn or short or missing chip/bent prong, etc.

So, to recap, his original speaker stopped working after screen replacement. He took the phone with him until parts came in. When he brought it back, the loudspeaker was making a hissing noise. Replaced loudspeaker with new part- still hissing. Tried another part from a different source- same problem.

Any suggestions?

Thanks in advance!