I noticed a ticking noise coming from the engine on my way to work this morning. It sounds like I'm riding a bike with a card stuck in the spokes. The ticking follows the revs of the engine and seems to be coming from the passenger side of the engine. It ticks in idle and in park while revving the engine. The car has ~230,000 miles on it. It's had regular oil changes and has about 1000 miles more to go before it's due for another. I checked the oil and while it's low, it's still between the dots on the dipstick. The noise went away after driving it for about 25 minutes but it came back when I tried it again later. I'm probably going to take it to the mechanic tomorrow, but I wanted to post here first to see if I can get a little more insight. Any ideas on what the problem might be?