[jetty-user] requests hanging, then behaving normally for 30 seconds, then hanging

I'm seeing some odd behavior in a custom app that embeds Jetty.  If a
server hasn't received a request recently, it will often take a very long
time to process the request- between 5 and 60 seconds- even for trivial
hello world handlers.  Then, once that request has returned, the server
will process requests at a normal, rapid rate, for precisely 30 seconds,
and then the next request received will take a long time again.  I'm
actually running two different custom webservers based on Jetty... they
share a lot of code, including the "hello world" handler that I'm testing
with.  But only one is experiencing this problem, and the most significant
difference between the two that I can see is that the problematic one uses
BlockingChannelConnector, while the ok one uses the default
SelectChannelConnector.  Other than the non-default Connector, I'm not
doing anything remotely interesting in the server setup- I'm not using any
Jetty XML files for configuration, and am essentially just doing a stock

Server customServer = new CustomServer(PORT);
customServer.start();
customServer.join();

I'm using BlockingChannelConnector for some servers because these server
variants should be receiving low numbers of persistent HTTP 1.1
connections.  The other SelectChannelConnector server (which functions as a
load balancer for the BlockingChannelConnector servers) will function as a
more normal webserver receiving requests from lots of clients, so
SelectChannelConnector seemed more appropriate.

So- does anyone know if 30 seconds is the default value for any Jetty
settings that might be related to behavior like this?  Or has anyone seen
similar behavior?