Unusual noise in 2004 Sequoia JBL system

[pfarrell20]

I just bought a 2004 Sequoia SR5 with the JBL 6-disc option. Frequently, but not all the time, I can hear a low level of background noise coming from the JBL system. Sometimes the noise will get louder as the volume increases. Sometimes it is more prevalent with one CD vs another. I don't understand this since CDs should not create noise. The dealer has already replaced the head unit and the amp is next. I am concerned that this will not fix the problem. I took the car to a car audio shop and they said it is just amp noise. However, I have 4-runner with an after market amp and I do not have this problem. Does anybody have any thoughts as to what may be causing the noise or how to diagnose this problem? Thanks

[mustang67408]

I would bet on the amp being the problem.
some of the 02-03 Sequoias , had a problem with a popping from the JBL system. It was the amp.