vibration noise when throttling

Hows it going guys. ive been on the site for almost two years now i dont post much, but im always doing searches and browsing the forum for any new information. I plan on getting pictures of the truck up this week. I installed a trd catback last night in 30 minutes thanks to the tutorials on it! Now the bad news, I have a 2008 V-6 with 45000 miles i have brought it to the stealership 3 times now for the same problem and they cant seem to fix it and the last time they told me it was normal which it deffinitly isnt since my dad owns an 05 and doesnt do it at all. If i start my truck and rev the engine there is no vibration noise but if i am in gear and step on the throttle there is a vibration tinging noise coming from the engine somewhere. They first replaced the cat's free of charge the second time replace the fuel rail system free of charge and the third time they told me it was a normal engine sound and that there was nothing they could do. Now i have the TRD exhaust and when i step on it the tinging noise overpowers it so you guys get an idea on how loud it is. It is really starting to bother me so i was wondering if anyone has any ideas or if it has happened to them. end rant

 

Are you in park when you rev it a little? Sounds kind of odd, maybe run a can of seafoam through it? How well has the engine been maintained?

 

I just bought a can of seafoam tonight. and im waiting to put it in. dump the whole bottle in the tank i just filled up? cause im not ready for an oil change yet. The truck has been maintained excelent oil changes every 5k with synthetic and toyota filters. never abused. and yes when i reve it in park no noise but if im driving and rev it, it makes the noise

 

come on no one has any ideas on what this might be???