Amp problem: 10 of volume

I bi amp Aloia 150.I amps. I noticed a just audible crackling noise off and on for a day then hardly any sound at all. I checked all fuses and they tested good. I get sound but only about 10% of the volume compared to the other amp. After troubleshooting it is definitely the amp. Any ideas?
Fuses are quite interesting. They can be partially blown and still conduct and look fine. The first order of business is to change them. Unfortunately, from the description, the likelihood is that you have a cold solder joint. That is a joint where the solder did not flow properly and electrical contact is either intermittent or being rectified. There are usually hundreds of solder joints within a component and so it narrowing it down is a tough proposition. Sometimes this type of problem can be exacerbated by humidity. This is a very hard problem to hunt down for the novice and usually indicates a return trip to the manufacturer or certified repair technician.
Not likely these are the fuses or output stage of the amp. Most likely it can be an input(driving) stage.
There can be (not sure if that's the case) shunting of an input driving stage and feeding the output stage with the small signal.
A professional tech can trace this problem pretty quickly.