Hi Mike,
Ambient Noise Reduction effects the input volume of the computer. (on Laptops)
This then tends to make that computer quiet in iChat.
Therefore if Ambient Noise Reduction is factor it will be because you Buddies are using Laptop Macs and have this potential setting. (Turning On or Off does not seem to make a difference).
The Connection Doctor (Video Menu) may help.
This show the incoming Audio and Video in a graphical form (two green bars)
If there is a problem then the bars will reduce in % and then go Amber.
Further drops will go Red and potentially disappear.
However this about about Audio being Sent not the Volume it might be.
I would try an Audio Only chat to see if the Bandwidth (Internet Connection speed) is playing a factor.
6:26 PM Friday; November 11, 2011
Please, if posting Logs, do not post any Log info after the line "Binary Images for iChat"
G4/1GhzDual MDD (Leopard 10.5.8)
MacBookPro 2Gb( 10.6.8)
Mac OS X (10.6.8),
"Limit the Logs to the Bits above Binary Images." No, Seriously