1998 Toyota Camry intermittent starting problem?

[big kev]

I have a 1998 Camry with about 140,000 miles on it. Normally, my car starts fine. There are certain times when it doesn't start. It's usually when the car has only been off for about 5-10 minutes. Also, when I make multiple stops on one trip, it will do it. I turn the key, the engine cranks, and it just doesn't catch. The car just dies, if I continue to hold the key, it will start to make a loud noise, similar to when you accidently try to start the car and its already on. When it has the starting problem, once I get it to start its just fine. It idles normally,800-1,000rpms, doesn't feel at all like it is going to die. I just put it in gear and I'm on my way. The car runs like a charm, doesn't idle rough or stall. I'm at the point now, where I have to try about 3-5 times before the car actually starts. I've recently changed the fuel filter, installed a new battery, spark plugs and wires, and air filter. I am really confused about what this problem could be. I have yet to be able to recreate it for anyone else, since it happens randomly and has been going on for about two years.Any help is greatly appreciated. I feel like I'm a wild goose chase trying to diagnose this problem.