General Loudness:
* Loud
* Booming
* Rumbling
* Roaring
* Thundering
* Clapping
* Shouting
* Screaming
* Honking
* Wailing
* Howling
* Blazing
* Resounding
* Echoing
Specific to Sound:
* Strident
* Piercing
* Earsplitting
* Raucous
* Cacophonous
* Overpowering
* Intense
* Fortissimo
* Amplified
Figurative Language:
* Obtrusive
* Loudmouthed
* Brash
* In your face
* Unmistakable
* Overshadowing
The best synonym to use will depend on the specific context and the effect you're trying to achieve.