i am having the same problem with my icom 706mk2g. The problem of the audio emitted by the speaker in TX occurs on all bands, mainly in AM and a little in SSB, and grows by increasing the RF power. However, it does not appear on FM. Tried checking grounds on all boards (loosening and tightening screws and securing contact points with outer case), but no fix. Is the only way to mute the speaker? Also I noticed that toroidal inductor L174 makes a loud hum on AM.