real mctube squealing

[luke691]

i recently finished the real mctube circuit from tonepad and prior to having put it in an enclosure (hooked up with jumper leads it was working fine, now when i turn the gain control too far i get a high pitched squeal. all cable is shielded except for power cables and the heaters. any suggestions as to what is wrong??

[luke691]

woops, i should ad that it only occurs when capacitor 7 is connected, when it is disconnected the problem is not present