Since you mentioned the voice enhancement button - I tried it.
I found out that during a crackling call, if I enabled "voice enhancement", the crackling stopped. It appeared to me that the volume was lower as well. When I disabled "voice enhancement", the crackling started again. It doesn't seem logical that the volume would be lower with "voice enhancement" enabled, but I do think it was. I'd have to check some white noise with a decibel level meter.
At this point it appeared in my test that enabling "voice enhancement", stopped the annoying crackling phenomenon. Hmmmmm?