something wrong. argh!

[neonrt 10+ year member]

i just got this amp. i dont see how it could be bad? its a refurb also. it hits hard as hell when it works... when i go up and downhill thats when it hits hard, then when i drive straight the bass output lowers incredibly. sometimes the bass will randomly kick in just driving forward, but mostly when i go up and downhill. its gotta be something loose but i dont know what everything is in place

i would start at the power source(battery) and work from there. if everything checks out, gotta be the amp.