HELP! Engine rattle/knock worsening since fuel additive/premium ga Options

[celicakitten]

Please help with any input as I'd like to get the knowledge of people who really know these cars! I just bought this car and am discovering some issues(as expected) that I'd like to sort out before going to the dealer or hopefully finding a good local mechanic to help me!

Here are some stats before I describe the main issue:

-97 Celica ST 5spd Stock-original engine/transmission
-192,xxx miles
Guy I bought it from recently replaced the:
-timing belt
-spark plugs/wires
-distributor(looks fairly new at least)

Everything works, passes emissions, shifts great, and idles perfect other then a little vibration when the air is turned off. What my main concern is that initially there was a slight rattle/knock on start up and occasionally at higher speeds(inaudiable if the radio was even slightly on). I tried to chalk it up to the bar that holds the hood up as the clip to hold it down in place was broke. 2 days ago I topped her off with 91 octane and a bottle of chevrons fuel system cleaner, and on day 1 the car seemed to respond quickly and perform even smoother.

BUT...

On day 2 the rattle/knocking noise became more apparent continually getting louder (although my paranoia/turning off the radio may also play a part), and is now almost constant! Only time I don't hear it is when the car is idling. I drove it 14 miles each way to work and back(mostly freeway) for 2 nights, and as of this morning I fear to drive it if there is a real issue with the engine. I put her in neutral and pulled the throttle to try and verify that the engine is making the noise...there's slight noise on the rev and then knock knock knock back down to a quiet idle. I had to replace the motor mounts on my old celica and this is nothing near the same noise, so I'm almost positive it's not that. When the engine cools off I will inspect the spark plugs/wires/wiring...maybe distributor? I'm afraid too many deposits have been loosened, but am curious if it could be anything else and what/if anything I can do to fix it!!! I know it's an old car and there's a good chance it may be the engines time...but I really hope not! I'd like to minimize my expenses until the time is right for an engine swap and still use this car as a daily driver around town. Any help or suggestions would be greatly appreciated!!! Thanks in advance!

This post has been edited by celicakitten: Jun 3, 2012 - 11:21 AM

[Hanyo]

Upload a video of the knock and where it's coming from. Us 6gcer listen to our engines every day so we can Tell u if anything is out of the normal.