1)How can I determine what the source of those 27 timers are?
Try to find instances of TimerCallback (for Threading.Timer):
!dumpheap -type TimerCallback
Then dump the callback properties (where callback address is the "Address" from the dumpheap output):
!do <callback address>
Then dump the Value address of the _target property:
!do <_target address>
That should spit out the object that holds a reference to the TimerCallback, which should lead you to where the timer was created.
I recommend checking out Tess Ferrandez's debugging labs, if you haven't already.
2)What does 13 dead threads mean?
My understanding is that a dead thread refers to a C++ thread which no longer has an active OS thread, but still has references and thus cannot be destroyed (C++ threads use ref counting).
A C# thread holds a reference to a C++ thread, and if your managed code keeps a reference to a C# thread, then that could be your problem.
This post on Yun Jin's blog might be of some interest to you.
3)One of my threads is marked as having a lock. If i switch to that thread and run !clrstack, i see the following - is it related to my timers?
That looks like a (System.Threading) timer thread waiting for its interval to elapse.