Louder on one channel

Luxman integrated amplifier has been in storage over one year. Now I take it out of box and when playing right channel is louder than left. I try switching cables and everything.everything. even meters show right channel moreoutput. What could be cause of this?
Have tried two different inputs, same result. Will try direct line straight when I reconnect it.thanks
One of the great audio questions. Even better than, why am I getting hum out of one channel? 
Not trying to be a smart aleck, but make sure your ears are not clogged.   I always have to clear my ears before and during long listening sessions.
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!