Confirming sub is torched...

Hi all,

I think my REL Strata III is torched and want to run the symptoms by the group to confirm.

Setup is Peachtree Grand Integrated X-1 to Wilson Benesch Arcs with REL Strata III connected high level.

The REL is connected with a Speakon connection at the sub, with red to right positive speaker out and yellow to left positive speaker out, with the black RCA connected to an AUX out (cable from Music Direct specifically for sub + Class D combos, hence the ground terminated in RCA for grounding purposes).
I am getting very loud popping/cracking noises through the speakers, at precise and consistent intervals, not quite a second apart.   Problem isn't the speakers - I've connected another pair, same issue.  It's the sub...

As soon as I unplug the sub's black ground RCA from the Peachtree, the popping stops.   But with only the sub's high level speaker outs connected I'm getting much lower output from the sub, and it's messy and confused.  No hum, which is a good thing despite the black ground unplugged, but unusable sub output.

To see if the Speakon cable is the problem, I substituted a standard Monster L-R RCA subwoofer cable and connected the Peachtree's preouts to the low-level RCA inputs on the sub.  No popping, but same minimal and messy output from the sub.

So high level with ground plugged in causes loud popping.  High level without ground plugged in cures popping but output is muted.  Low level output is muted.  

Fuse is fine, I checked.   Sub driver looks fine from the outside - surround isn't degraded, and it doesn't sound blown.  The output is muted and messy, but not scratchy or blown.

What's consensus...sub's amp is done?
Bae07185 77e2 4002 80d8 1cd5774ecefdbcgator
I had this happen to a KEF sub years ago and concluded that the filter caps in the power supply were shot. It might be repairable by a good local shop, depending on what the cap values are, though most modern caps are available through Mouser and other suppliers. It could also be one or more power transistors or even a broken trace on the PCB or a faulty connection. That’s my best guess without knowing much more; more hands on troubleshooting may be required.
Thanks for the reply stevecham - I got this unit used a couple of years ago as part of a multi-component trade on CL.  Implied value in that deal was maybe $350, so my investment isn't large and I've gotten 2 years out of it.  If we think a local shop can diagnose and fix for less than a mortgage payment, I'd do that.   I'll see who in my area is good for this type of repair.