no problem
if the problem is still there with out the rca connect. then i will look into your gain setting. if your LEVEL is too high up. it will pick up any little vibration from the motor or anything.
i would try setting the level all the way down nd if the "hmmm" goes away. then try hook back up the rcas if it still come back. try running new rca but dont install them. just run from the head unit back to the amp, and if there is no "hmm" then install those new rca and like said above route the far away from your power wires.
- also if you screw an amp down to metal (car body) some amp will pick up ground noise. and cause a "hMMMMMM sound"