I bought a wrecked 05 gs 500f I was appy to see it had 69xx miles. only cuz i know these motors last FOR EVA!!!!!!!!  but turns out that the motor  has a tapping noise to it.  Then I look in the FS section and I see an 04 with 4xxx miles with a blown motor.... whats going on here. I thought these motor were bullet proof? 
I have not had a gs in years so i'm a little out dated when it comes to faults of these bike.  has the quality of them gone down?

I've got 40,000 odd kilometres on mine and its been over twice I'm aware off. Once I did and I bought it as a write off from a lay over. Other than fork seals needing to be change almost as soon as I got it (and it had less than 8thou kms at that point) and a dead gasket on the timing chain adjuster (Just a recent event) never ever had an issue.
Mines a 07 F too.

honestly mine makes funny noises all the time (sounds bad i know) but for over 6000 kms, using all gears, and the whole rev range (when its warm, i dont wanna cause problems) quite regularly... nothing has gotten worse, and that's with  a couple low speed drops.... so i assumed it was just the model lol

06 gs500f (swear its the 07 paint job though rego papers say 06)

make sure it has oil, have you checked the valves?

A video of the sound would enable us to tell you what it is and if it is serious.

Fairly reliable engines unless they run out of oil.  Then they very quickly assume the properties of a small boat anchor.

Anyone had a GN250? There was a bike with oil issues. lets have a bike that holds 1.3Litres of oil. A steep slope meant the dam thing would starve. Other than it would try to kill you if it saw gravel it was a good learners bike.