There is a big difference in sound between a timing chain slapping on the cover and a rod knock. I agree with Oatmeal, but piston slap and rod knock sound slightly different. Most people don't even know what piston slap sounds like, unless you are a mechanic and repair lots of engines. Piston slap in the 22s is NOT nearly as common as mentioned, at least according to my research. If you can move the guide it's probably worn thin or broken. The timing chain slap will sound loud at start up and sound more like the "tick" of lifter or rocker arm and close to the front of the engine. Loose rods will sound like a knock down by the oil pan and tend to continue from startup while driving. Worn rods and timing chain guides are fairly common on high mileage 22s. Using water when you can't find a leak is usually a head gasket problem or a cracked head. This is fairly common any time after about 100K miles. A leak-down test will most likey tell you if you have a blown head gasket or a cracked head. If you suspect it's a rod bearing, you can put in a can of STP Oil Treatment, if the knock goes away or quiets down, it's most likely bearings. I've heard of a knock caused by too much end play in the crankshaft, but I don't think that is any more common in the 22s than piston slap. TJMHO.