#1
I picked up a Fender Champ 600 due to some travelling I have coming up. I demo'd a floor model at the store with a Jazzmaster, and it sounded good. It did not exhibit any of the following problems:
I got it home, opened mine up, put the volume half way, and fired it up. I tried my RG2550 w/ mid gain Dimarzios, and breakup got pretty bad. Then I tried my stock G&L Legacy w/both input jacks and the farting continued, even at lower volumes.

I've heard some people resort to swapping the tubes out and speaker to fix these issues.

Any advice?
#2
if its new I would just return it for a new one, but if thats not an option maybe a tube or speaker swap would be good, but you should probably have a tech look at it
Gear:

MIA Fender Stratocaster
Jackson Kelly KE3
Ibanez Universe
Marshall JCM 800
Orange Jim Root Terror
Mesa 2x12
Ovation Custom Balladeer
pedals and such in profile
#3
go take it to a tech.
Gear:

American Strat
Epiphone Valve JR head - Volume Mod'ed
Custom 1x12 with Private Jack speaker
Boss BF-3 Flanger
Boss DS-2 Distortion
Boss MT-2 MetalZone
Ebow

Gretsch Acoustic
#4
Tube-swapping isn't/shouldn't be a last resort. It's important to keep your amp in tip-top shape. Especially if it's been played by other people, some of whom haven't the faintest about how to treat a tube amp. But if it hasn't been long, I'd bring it back to the store and get it sorted out with them.
#6
there is a very good chance it is the tubes

but yes, take it back to the shop
if you love bbe products join the "i heart bbe" group. kthnx (click link below)
http://groups.ultimate-guitar.com/ilovebbe/

Quote by Dempsey68
get a cheap marshall... my MG15DFX has a button that simulates the sound of one of the expensive tube marshall amps.
#8
Update:
I just bypassed the stock speaker and connected it to my 412, and it sounded great. I guess i can rule bad tubes out.
#10
Did you feed it grilled onions? JK
This is why you bring your guitar to test out amps. The stock speakers aren't usually the best in low wattage budget tube amps, but yours could be faulty.
I wondered why the frisbee was getting bigger, then it hit me.