I have a Yamaha electro-acoustic guitar and recently bought a Fender acoustasonic 15w amp. It worked fine for arround 10 days, but now all I get is very aggressive, sometimes pulsating static. I checked the wiring on the guitar but found no loose wires. Is there anything else I can check, or is it the amp that's defective?
Looks like the OP found the issue but wanted to give some tips for others that may have similar problems.
When looking for an issue like this it is a good idea to figure out exactly where in the signal chain the issue is.
If you have a guitar > pedal > pedal > amp the issues could be in any of the cables, the guitar, any of the pedals, or the amp itself.
I would trouble shoot this issue by eliminating as much of the stuff between the source (guitar) and the amp by plugging the guitar directly in the amp with nothing between.
If the problem remains, try a different cable. If the problem remains and you have another guitar and or another amp, swap one of those out. At this point you should have narrowed it down to the amp, or the guitar.
If plugging the guitar straight into the amp works you know the issues was in a pedal or in a cable. Slowly add pedals back in until you find the issue. This technique can be expanded out to any size and complexity of a signal chain.
I hope this helps.
As the OP remembered, it's always good to consider the last thing that you changed. Good chance the last change has something to do with the new problem.