Driving a Nissan Sylphy.
Lately I noticed a vibrating noise coming from the engine at low revs (intermittent) whenever the air-con is switched on. At higher revs, the vibrating noise disappears. Without the air-con switched on, there is no vibrating noise heard. Any idea what could be the problem? Is it serious?
Car COE is expiring in May 2016, so I don't want to spend too much money on it.