ERJ145 APU Help Please
 

With APU Bleed Off - APU Barks. Bleed On, no problems.

Any suggestions of what to check to resolve this problem please!?

What is your APU EGT doing? Could be compressor stalling... The 135/145 APU doesn't normally "bark", although they are known to start smoking and possibly howl like a banshee when they are getting near major overhaul :}

If it's compressor stall, you could have compressor damage of some sort, so worth getting checked out.