Mis-behaving crossover/preamp

[xeclipse]

Hi guys,
I built this crossover and preamp using tl072.12dB/octave low pass crossover at 106Hz for the first opamp and a 24dB gain preamp for the second opamp.Now its working but...a slightly audible hum when the gain knob is halfway up,the hum disappear when the knob is all the way up or down.The woofer cone moves considerably when the knob is turned with no input signal.There's also a whining noise a few seconds after the power is switched off.
Is there something i overlooked?I will appreciate your help in solving the problem.
Regards.

 

[xeclipse]

The gain stage

I got it from esp projects.
I made the following changes:
input r28:1k
vr4:200k
r19:12k
bypassed c5&c6 and put a 10uf cap after the 100r r28.

 

[xeclipse]

The crossover

I used the crossover calculator to get the r&c values(not the showed values).I just realised my mistake:i used 2c instead of c.How does this affect the crossover?