Louder on one channel

Had this issue.
switch the speakers, and listen

Left  speaker is at an opening to a larger part of the house, right is in a corner, right always sounds. Better, it’s in a corner, where as the left loses some oomph to the stairwell, and open part of the house.

could just. Be acoustics. as mine is.

i switched the speakers so many damn times, but always the same, 
i came to the conclusion it’s the “ROOM and acoustics”
not the amps, or speakers, cabling. 

Just my my two cents 

You didn't say how big is the difference between the two speakers.
Over the years, I have had this type of issue twice, but the difference was subtle and it moved the soundstage towards the left (my left speaker was producing less sound):
a. Once it was fixed by pulling the speaker few cms out, and changing the toeing to match the other speaker.
b. Most recently, it was one of the speaker wire connectors connecting to amp. Once I replace the speaker cable, problem was fixed.

All the best!

make sure your ears are not clogged.

Could clogged ears affect meter readings?