Rookie Question

I have a '90 Corvette, stock engine not ZR-1.  The car has 61M on it and I don't have complete
repair records.  My problem is that the engine has developed a valve/engine rattle.  When I excellerate
a little strong I hear a rattle coming from the engine.  Kind of like a knock but more like a rattle.
 
I use only BP Gas ethyl rated at 93 octane.  Just got engine oil changed for 2nd time with Mobile Synthetic.  Have put in injector cleaner but did not let the cleaner go thru full cycle of tank due to expense of full tank fill-up.  (Kept filling up after 1/2 tank.)
 
I don't know when last tune up was done.  Think this is next step?  Appreciate advice.  Thanx

I don't have much experience on the injected engines but it sounds like the knock sensor is at fault.

A tune up surely wouldn't hurt. The noise you're talkin' about, can be a timing issue.

Have you throttled up using the linkage with the hood up? You might zero in on the tunes this way...
 
How many miles on the vehicle?

Sounds like EGR is not working and what you are hearing is detonation. Also, check your ignition timing by disconnecting Set Timing connector and then check with a timing light.

Thanx y'all.   Appreciate timely replies....  

Have appt. next Weds to have mechanic tune up my '90 and especiallly check the timing.  Hope that
will take care of it.  Probably going the plugs, wires etc.  he said could do with AC Delco parts and get
her done for $250.00 - $300.00     (He takes plastic thank God, after the new Borlas and labor I'm Tap City.
 
Again, I appreciate everyones input.

Well, got the tune up but still a little knock/rattle.  Mechanic advised then it probably is bad gas.  Suggested I put some Octane 104 in the gas tank.  I bought the Octane 104 Maximum and added it.
So far so good.......

It's not the gas. By putting 104 in, you are probably covering up the problem. Did you have the EGR system checked out? EGR valve not functioning will cause detonation that you are hearing.

Thanx mech259.  If this hasn't cured it (haven't driven it since week-end) the EGR Valve
will be my next stop.   Appreciate info.

Mech259 you were right on the money.  The valve clatter had subsided slightly but still there.  I took it into my mech. and he checked vacuum and all and found the EGR Valve plugged.  New one on order.   Really appreciate your tip.  Thanks.