McIntosh MC2152 power amp technical question

My MC2152 suddenly acting up. When I use the XLR input the right channel makes popping sound when power off. To make the situation worst, the sound coming from this right channel is slightly lower compared to left channel which resulted in uneven sounds: left sound louder than right. IF I use the RCA interconnect the sound is fine and no speakers popping noise when powered off. I can settle by using the RCA interconnect and move on but i want to use the XLR input for better sound quality.  

Could it be the XLR right channel input connection defect? Or the electric board holding the XLR right input is defect?  Any technicians here in the community, your inputs would be greatly appreciated.  

thank you in advance for all your suggestions/help. 
No responses. If I were you, I would contact Mcintosh. 
McIntosh said to being in for service and who knows how much they’re going to charge. Arm and a leg!!! 
Try swapping the cables and see if the problem moves to the left channel!
Is this the 70th anniversary amp?  

As suggested try swapping the cables.  Could the problem be with the pre amp? 
swapping cable and its move the left: meaning when i switch the cable to left speaker (with the right jack) the problem deferred to the left channel.  Which means the right channel input jack is something wrong. 
Yes, this is the 70th anniversary edition.  McIntosh is not very helpful and not backing up their products.  I called and they dont help me troubleshoot, all they want is for me to sent in for service.   I bought it second hand so they said warranty is not transferrable.  
I used to own a ton of Mac.  Send it in! If it is a manufactured fault they will repair it for free, regardless of how many owners there have been.  If you have to pay for a repair, it will be done right and with a warranty.  Their rates are no more than your local repair shop. At least that has been my experience.  They are awesome to deal with.

@normansizemore  i spoke with them this morning they told me no warranty since im not the original owner. I’m not sure if this is a defect or not.  So you dont think their repair rate not that more expensive than local McIntosh service? 
If you swapped the cables and the trouble moved to the left channel why do you think the problem is not the cable or the preamp output? Did you swap both the cables at both ends from preamp out to amp in?
As stated above, if you swapped cables and the problem moved from the right to left, it is not the amps input, but a cable or the preamp / source...
No guys.  Even not connected to preamp still making popping sounds to the right channel. I’m bringing to mcintosh service center.  McIntosh don’t recommend sent it in because its so heavy and transit across country could damage the amp. 
I am really surprised at Macs response to your service question.  For decades, no matter who owned the unit, if it was a manufactured defect, they fixed it.  Period.  Additionally, their service rates were always in line with third party service agencies, and Mac service was top drawer.  Obviously, the end of an era for Mac, and a huge disappointment to those that have supported the brand.  
@normansizemore yes i am very shocked to find out too.  This is an expensive unit and they didn’t offer me any help at all.  They told me warranty is not transferrable and that’s the end.  Even when i asked to sent in they tried to steer me away.  The whole thing i didnt feel like they’re really stand behind their products.  I am very disappointed in the way they handle this situation.  Usually every other company warranty go with the item until end of warranty term regardless of owner.   Anyone else have any input about this?? 
Actually, most manufacturers products, new, come with the manufacturers warranty, to the 1st owner only. There are exceptions of course. The fact that they immediately told you to get the piece to them, shows me they wanted to take care of the issue, even though at a cost, which is reasonable to me. And honestly, this is a reason, some people will spend more, for a new unit, as opposed to used. Hope it works out.
@mrdecibel they didn’t wanna take it. They told me to bring to near by service center.  I want them to fix it but they don’t want to - they basically steer me away from sending in.  Most big companies will honor warranty regardless of how many owners.  Take Apple for example, iPhones warranty follows the phone regardless of how many owners.  I’m just saying this is a $15k amp and it’s only 8 months old.  
mrdecibel is of course correct.  However being in my late fifties, I harken back to the McIntosh of old.  I have owned a MA-6100, C-26, C-27, C-28, C-29, MC-2300, MC-2105, MC-2505, MR78 and none of it purchased new.
When I bought my MC-2300, it was nearly 10 years old, had a little noise in one channel. I called Mac, they sent me a shipping crate, a box and instructed me on how to pack it.  (I paid for those materials).  They repaired the amp and provided notes and test results.  It had a bad filter cap (about the size of a beer can) which they replaced at no cost.  They also replaced the good caps so that everything was a matched set. My 2300 was an early run, so my cap issue was a known problem which was remedied in later production.
So, because of that there was no cost to me.  That is the McIntosh that I am talking about.  First rate products, impeccable build and stellar service.
They are still the ones I would send my amp too, but their response to you clearly indicates that the old way of standing behind their products is gone.  I guess that it being “Mac” I expected more, I think anyone who’s buys Mac expects more.  
@normansizemore that’s exactly i would expect from Mac too. To stand behind their products and people buy an expensive product  they expect stellar service.   Like luxury cars and Toyota.   I’m disappointed in Mac.  Prolly wont buy anything from them anymore.