I just bought my yamaha gigmaker erg121c starter pack less than a week ago (2 humbucking, 1 s' coil, 15W amp, 1 volume knob, 1 tone knob)

when i keep the tone knob on full, if i increase the volume on any channel on my amp(clean or drive) i get a very unpleasant buzz. if i turn the tone knob and bring it to 0, the buzz vanishes. adjusting the drive-gain knob on the amp does not make any difference (though it does add an even more unpleasant squeal if increased too much)

is this normal or should i get my guitar or amp checked???

please help.
It sounds like a problem with the tone pot (control). Take your guitar to a shop and play it through other amps. If the buzz is still there, show it to a tech and he could replace the pot for you.
since the guitar came from a starter pack, it may not be properly shielded around the electronics (i.e. wiring and pickups). you could go to any guitar shop and buy some copper shielding tape and put it under all the electronics. that should stop the buzzing. and it it doesn't, there may be something wrong with the wiring itself. and if that doesn't help i would take it to a repair shop or something. if you can fix it yourself, always do that. most repair places charge an arm and a leg.
GAS List:
The buzz is either shielding or grounding. Make sure you use a properly grounded three prong power cord and power supply. Get away from florescent lights, tv, computers, etc. The squeal is feedback, this is normal. Keep your guitar away from the speaker, don't face the speaker at high volumes, move to the side of the amp.
The drive-gain knob adds distortion, another sound option and highly desired by rock players. If you turn it on too high you will get feedback especially close to the amp or loud in a small room. You will learn how to deal with this and use it properly. I recommend the Ultimate Settings thread on UG. Good luck.
I had the exact same thing with my [unnamable] starter pack, they generally are pretty poor quality it seems, regardless of the brand.