Musical fidelity amp x-a2, one channel intermittent crackling / fading out, any ideas?! Tried swapping source and speakers... Many thanks -chris

Perhaps you must check out wires for speakers and contacts on receiver and speaker.

There are several issues here... You can connect subs in parallel BUT they need to have a crossover built it otherwise you are sending highs and mids to the subs which won't like it. Properly set up, there should be NO crackling on either channel.
Make sure that no clipping is going on, including in the effects. A set of headphones is a GOOD idea when analyzing problems. Twelve inch speakers are pretty marginal for 300 watts... I have used 15's and 10;s on my PMP3000 and PMP5000 units with no problem at REASONABLE sound levels. With 15's we can run at 95 Db which is OSHA limits... My PMP's were beyond repair units and I have repaired them... got a good deal on them. PLEASE read my tip on here about channel A of the PMP mixers. IF you use Speakon to 1/4 inch speaker cables, THE sleeve of Channel A is the "hot", not the tip of the plug. It is easy to get this grounded and kill channel A of your amp. There is NO mention of this in the user documents and I discovered it when repairing the units. Should you get a failure that pops the fuse, DO NOT replace the fuse until the internal damage is repaired. A lot of craclking can come from blown speakers. Swap your sides and make sure the problem is not with a particular speaker. I had a Peavey that was crackling and found the noise was the logo on the grille that was rattling...

Is it on all audio sources or only certain ones? Have you swapped the speakers Left-to-Right to isolate the speaker from the signal chain as a cause?

If it's only an analog source doing it I would suspect a bad audio cable or a switch contact somewhere in the signal path. Typically, it might be a switch you rarely use, like a Tape Monitor or Mute. It's wise to occasionally (with power OFF) manipulate all manual controls throughput their ranges a number of times to wipe oxides from their contacts.

It depends on what wrong is with the receiver. If there is bad DSP (digital surround sound processing) board better to buy new receiver. If it is just bad channel it can be repaired below or about hundred dollars. It could be also just simple cold soldering joints. You need to bring it to a repair shop and get an estimate.

Could be caused by a burnt resistor in the channel of the main power amp. You should be able to see it. It might have been caused by the faulty speaker wires.

more than likely you have a bad transisitor on that side and the frequincey is distorted there's not much you can do except take it back if it's new or take it apart and check for the bad part but if you do that you had better know what your doing!! it may be just 12 volts but thru an amp it's a nasty shock

Would check your balance settings. Make sure your not balanced more to left than right. Next i would try to swap over one of the speakers from right side to left to see if it crackles. If not replace left side speakers.

easiest way to see if the left outputs have gone is to swap the right and left speakers over. if the left works out of the right channels you know if the set has had it.hope this helps

Make sure your speaker wiring does not come close to the 12v power cable running for your amplifier. If your amplifier's 12v power cable runs on the drivers side of the vehicle, run your speaker cables on the passengers side and make sure your tweeters have a high pass filter to stop any pickup of engine sound (When you are driving you *WILL* notice it at high RPM. a HPF (High Pass Filter) will also stop those nasty hissing sounds on S's.

Audio output electrlytic capacitors have dried out, locate & replace them if you want your sound back, it's cheap but not easy.