It's hard to say what exactly is going on without being able to investigate the affected machines, however this appears to be some kind of "ping back" mechanism using DNS.
Per DNS specs, query failures must never be cached by a resolver cache, therefore every request for these domains hits the authoritative name servers. I'm not confident why they do that but clearly there's very likely something on the other end counting hits on these and gathering stats. If it's sophisticated enough, it could even be sending information by encoding it in those name lookups.
You should try to identify the source of these requests and make sure the computer/server is not infected with spyware/malware. You could also configure your DNS resolver to send all queries for the domain (ad.broadcom.com) to some dummy/non-existent servers so that the queries do not reach the intended destination.
P.S.: Is all these queries end up on a broadcom.com domain which is a pretty big US corporation, so I wouldn't be too worried - you should check if a Broadcom utility does it and maybe ask the company why... But if it was going to some shady domain that would definitely be worrying.