2000 Mustang GT 4.6 Engine Help!!!

I have a 2000 Mustang GT 4.6 Liter with 74,000 Miles.
Recently I have noticed a "tapping" noise in the left side of the engine. This happens when I'm at about 70mph or 2000rpm. The noise isn't bad enough to be a rod knocking, but I'm thinking it might be wear and tear on the valves????? I've had the valve covers off myself and the roller rockers seem to be fine. This noise seems to be coming from the valves/lifters. I'm just wondering if anyone has had this problem. I don't rough ride this car and this shouldn't be happening to a car this new!!!
Any sugg's?

These are really hard to diagnose without hearing the car, but here goes.

For starters, how fast does it knock? as fast as the engine or slower?

You don't have rockers, so to speak, just cam followers.

It could be an injector sticking, it could be a valve tap, it could have something to do with the chain drive for the cams, it could be in the accessory drive somewhere, or it could be a scored piston (not likely). There's a lot of possibilities.

It knocks in sequence with the engine but much much slower. It's not very loud... yet. It actually does it more when I'm coasting at about 70mph (with no tension on the engine) and then when I give a little gas.... It almost sounds like a sewing machine, but not loud and not fast... almost like a minute jake brake.....

We used a stethoscope and (if you're looking at the valve covers from standing in front of the car... it's the set on the right/driver's side and the area closest to the driver).

I just want to do some pinpointing before I have anybody else look at this... The mechanics around here are full of crap and since I'm a girl they all want to sell me a new engine. I'm far from stupid and I plan on fixing this myself... I just don't want to fix something that isn't wrong and I don't want to tear down my engine and have something completely different than expected.

It's like one of the valves/lifters is stuck. I added some Lucas Oil to my Penzoil to see if I could break loose a lifter/valve. It didn't work... it has progressively gotten worse in about a month. This car is mostly highway driven.

Any chance it could be a cam bearing on that side?

Did you listen to the injectors?

If you pull the V/C again, try removing the spark plugs and turning over the engine by hand and listening for anything knocking, scraping, or anything like that. Check everything for play with the motor in various positions.

I haven't worked with mod motors much yet, do they have a lifter holding one end of the cam follower like most SOHC setups? If so it could be a collapsed lifter letting the follower chatter around.

I haven't worked with mod motors much yet, do they have a lifter holding one end of the cam follower like most SOHC setups? If so it could be a collapsed lifter letting the follower chatter around.

modular motors do have a small hydraulic lifter in the head opposite the valve. you could be right there. i hope it's not a piston... doesn't sound like it tho.