Head requests failing, locking up client

I have an existing production server that is having some problems. When I use elasticsearch-ruby client, and do an "exists" request.. it performs a head check to see if the ID exists.. (this is how it works in the /plugin/_head as well). On /plugin/_head and using CURL, and using my local client, this behavior has been seen.

It doesn't happen but about 1/100 incidents. When it happens, it locks up the client. and the process hangs.

I have checked every permutation I can. We have determined using packet traces that the request goes to the ElasticSearch server.. but the ES server does not reply with a valid packet. It returns an empty packet.. which hangs the client.

We are down. We have been down for 2 weeks. I"m lost as to what to do next. It is clearly an ES server issue. 1.7.4 on ES.