I've got a 1988 TRX350D that is making a popping noise in the front end. I jacked it up this afternoon and it's silent when turning the handlebars back and forth. But when I rotate the wheels it pops a little. When driving it straight forward it sometimes makes a slight pop and then stops. But when driving it forward with the wheels turned it is loud and constant. What are some common failure points on these that may cause this and can you still purchase new front end parts for them?