Varnish serves 503's for 10 second intervals a few times a day

[Jennings, Raymond]

There has got to be a way I can drill down as to why Varnish does this.
 Looking at the varnishncsa output I am seeing 5 to 10 second intervals
where all requests are returned as 503's  When I look a the backend apache
servers there are ZERO requests in these time periods.

I see nothing in syslog with any varnishd messages or any other network
error.  I believe this is internal to Varnish but cannot find anything.
 Any clues how I can go about digging into this.  This is a production
system so I cannot modify code but I can insert VCL (C inlined is fine)
 For now I tried turning on varnishlog (already running varnishncsa.)
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