exhaust / service

[chileno]

hey guys, just wondering after i got my so-so exhaust put on my turbo. I found that when i have it idling in neutral, and put down my foot to give it revs(hard) it kinda back fires. Anyone else had this.
Also took in my car for its 30,000km service - $400, for oil and sparkplugs - rip off i reckon.

[Dave]

just un burnt fuel in the pipes burning of man. does it do it aswell when your compression brakeing or dont you drive that hard?