On Alfa number 15
AO Platinum Member
Join Date: Dec 2005
Location: United Kingdom
I had a similar think on my Golf, it is caused by the perforated tube in the silencer rusting through, the gases coming out then carry the packing material out.
I wouldn't say it was harmful to the car, but you might find the exhaust gets louder the more of it comes out. I doubt it would affect power much though as a straight through pipe is already pretty efficient, and unless it gets silly noisy (unlikely) it should still pass the MOT.
I kept getting asked if I had Tina Turners wig stuck up my exhaust.
If I were you though I would start saving up for a new exhaust, because if the perforated pipe has rusted through the silencers probably will rust through as well in the near future.
You will never be cool driving a Vauxhall.