ticking on acceleration

I just picked up an 04 GT 133k miles last week. Got it for a steal, but it was throwing codes for the cats. Ordered a Summit O/R H pipe for it and put it on yesterday, and it's running much better now. But the only issue I'm having is that on acceleration it has a pretty loud ticking noise, which gets louder the harder you get on it. I've done some searching and it seems like most of these cars have a ticking at idle, as does mine. But it sounds like it goes away for most people above idle. Is this sound normal and being magnified by not having cats, or is it something I should be worried about?
 
You should not be having a tick on acceleration. That would most likely be detonation due to bad gas or a bad tune.

How did you turn off the CEL after adding the o/r mid pipe?

Haven't yet, I'm planning on taking care of that when I get a tuner. The light has been on since I got the car so I've gotten used to it. I'll put some 91 in it and see if it goes away, but it's just running the stock tune.

I'm hoping it's just an exhaust leak. It ticked at idle before the H pipe, but I never noticed it accelerating until now.
 
Ticking is usually attributed to these common issues:

-Exhaust leak
-Loose Spark Plug
-TOB on manual cars. the Throwout Bearing can give a more of a slightly chirping sound without the clutch pressed in, then with slight tension on the clutch it goes away.

Couple of questions to help decide what it is:

Is it more audible from the engine or from underneath the car?

Does the tick increase with RPM's?

Are you sure you used a new gasket on the passenger side manifold with the new midpipe?

HTH,
 
I dont know what kind of research you've done, but ticking at idles is NOT common on these motors.

There are 3 possibilities:

1.) exhaust leak - like others have asked, did the tick exist before you messed with your exhaust? Do you smell any traces of exhaust insde the car?

2.) detonation - do you know how many previous owners the car has had? Any one of them could have had a higher octane tune installed without you knowing about it. Using regular on a tune specific for premium will often produce detonation

3.) a plug is starting to back out (as joshjwc mentioned) - I noticed a ticking noise during accel that became progressively louder over time until my plug finally blew out.

Is it a "tick" or a "rattling" (like a pebble in a tin can) noise?
 
This year model mustangs and F-150s had a bad problem with blowing out the spark plug because when the heads were made they did not tap the threads correctly.