Strange exhaust blowing noise..?

[Usual Suspect]

Right then you lot...
..I'm driving home the other night when suddenly there's exhaust noise coming from the engine bay  
 This is a kinda 'muffled' blowing noise..??  
 (It was dark, so could not see if the old girl was smoking out the back)
 Power had dropped too..so limped home at about 30mph.
 Went to bed somewhat confused..that exhaust noise was more like blowing back into the system somehow..??
  Well..next morning (dark again)..I turned the key, she started promptly as usual, & no exhaust noise...all normal 
     BUT..What the hell made that unusual blowing noise, & loss of power ??
  (No more problems since, but my suspicious mind tells me that maybe those exhaust gases have ventured back towards my air-filter..or maybe that's impossible..?)
       I do not know...but I bet one of you lot does..??

[dieselj]

once happened to me with my trusty little micra. loss of power and all that.
pulled of the motorway and had a look around the car.
there was a giant hair ball hanging out the exhaust!
pulled it out.
and it ran like a good un!
in fact, sounded ace after that!
not saying this is what happened to you. but it sounds alot like what happened to me.

[ffrenchie]

What engine are we discussing ? It could be an injector seal if it's a diesel but they don't usually fix themselves.

[Landmark]

Could it be something that is occuring when the engine/exhaust gets hot?
Griff