Amp tripping circuit breaker.

I am a certified electrician. And I believe part of the problem is the AFCI breaker since it is known to be a common problem with them and GFCI types. Also confirm if you are using a 29 amp breaker with at least 12 awg. Wire otherwise you are overloading the circuit with your rack setup. Just because the breaker says 20 doesn't mean the romex in the wall is suitable for such a load. 

I would find out what the amperage is under load with. Conventional amprobe  at the panel. And if you are exceeding 16 amps then you are using more than the breaker can handle for long term use. 

I would recommend a dedicated circuit with at least 12awg  10 would be best. and have the electrician or yourself balance the loads between your 2 legs at the panel. By moving some wires around to come up with the most balanced load on your hot legs. 

I have seen tripping on breakers from loose connections both in j boxes and receptacles. And in some cases the wires can overheat and melt before the breakers actually trip.

Hope this helps.
 

I meant 20 amp not 29 amp breaker.

Yes it’s 20 amp wiring.

Trouble shooting 101...replace the least expensive item first.  Replace the breaker and see what happens. 

NEVER change 2 things at once.

Ground at wall outlet?

I can understand lost confidence in the amp, but, the advice to replace the breaker first is the best.

If electrician does it, he/she can also test ground, at the panel and at the wall outlet.

That will tell you whether it was the ground, breaker, or the amp.

IF, after replacing breaker, ground confirmed, with amp connected, turned off, new breaker trips, curious indeed. Test that before electrician leaves.

Do you have any other equip you could substitute for amp, to see if problem goes away? 

IOW, think like an electrician rather than as an audiophile.

New amp after circuit confirmation? Always fun. Keep in mind, you won't be able to sell the existing amp unless you confirm it was the breaker, not the amp. Another reason not to change two things at once.