Sporadic 503 errors with 3.0.2

[Bryan Stillwell]

I'm seeing sporadic 503 errors that I'm wondering if someone could
help me with.  If I read this right, there appears to be a problem
with the backend:

  151 VCL_call     c recv lookup
  151 VCL_call     c hash
  151 Hash         c /2le1ert_th.jpg
  151 Hash         c s7.tinypic.com
  151 VCL_return   c hash
  151 VCL_call     c miss fetch
  151 FetchError   c no backend connection
  151 VCL_call     c error deliver
  151 VCL_call     c deliver deliver
  151 TxProtocol   c HTTP/1.1
  151 TxStatus     c 503
  151 TxResponse   c Service Unavailable
  151 TxHeader     c Server: Varnish
  151 TxHeader     c Content-Type: text/html; charset=utf-8
  151 TxHeader     c Retry-After: 5
  151 TxHeader     c Content-Length: 419
  151 TxHeader     c Accept-Ranges: bytes
  151 TxHeader     c Date: Thu, 27 Oct 2011 04:17:57 GMT
  151 TxHeader     c X-Varnish: 1163340533
  151 TxHeader     c Age: 1
  151 TxHeader     c Via: 1.1 varnish
  151 TxHeader     c Connection: close
  151 TxHeader     c X-Cache: MISS

I currently have the backend configured to use a single IP, which
points to a pair of load balancers that distribute it to numerous
webservers.  It works great 99.99% of the time, but that other 0.01% I
get 503s.

Is there any way to get more details on what the failure with the
backend is?  Was there a failure connecting to it?  Bad response?
Timeout?

I almost think this is a varnish issue (seen on both 3.0.1 and 3.0.2),
because I'm seeing the problem on all my varnish boxes, in multiple
data centers, pointing to different backends.  The only other thing I
can thing of is there might be an issue with having the load balancers
in between varnish and the backends.  I plan on testing removing them
from the equation by just referring to all the webservers individually
soon, but I haven't gotten to that yet.

Any help would be appreciated.

Thanks,
Bryan