amp makes a noise like feedback then cuts out :S

[JoeG07]

been running a sony amp off an alpine headunit for a year but just last couple of days its started doing this thing where it turns on and works fine, then suddenly makes an aweful noise like feedback for a second then cuts out. because its inteermitant, i cant find a fault anywhere! I havnt touched any settings or anything. any ideas??

[alexperkins]

Check the ground. That can cause all kinds of problems