Hi TJ...
To my ears... Solid State amps, like your 370, always seem to have more white/pink noise type hiss to them than tube amps. Tube amps always seem to have more hum.
Excessive hiss, where excessive is certainly subjective, should be looked at by a tech. Cold solder joints, out of spec resistors, and just plain lousy connections that can develop over time in amps constructed like the concert series can happen with age.
If you just got the amp, live with it for a while, especially in a playing situation. The hiss of some amps, while it might seem excessive in a "bedroom practice" situation, can easily be masked out by a drummer in a loud playing situation.
The 370 was meant to be played loud. There are some solid state amps that seem awful hissy at low volumes, but not when turned up - like the K200B series of Kustoms.
On the other hand... if this is a recent acquisition, then it is possible that some previous repair might have been accomplished with less than low-noise components, and replacing those might be worth the effort.
But to answer your question, in my experience, solid state components either work or they don't - nothing like the gradual decline in sound quality like you get with tubes when they wear out.
