Writing - Onomatopoeias in Dialogue

How would you format onomatopoeias - the sounds, i.e.THUD - into the middle of a dialogue, specifically one person's, or midline.

Would you:

1)keep it inside the quotes
2)give it it's own paragraph
3)stop the quotations around it

Serious help is appreciated.

Harold slogged out of the tub with a certain charming amount of lethargy only to be rewarded with a curious sliding sensation between his buttocks...

~ssssssssssssplortch~

"Oh my...  I seem to have prolapsed..."