[tor-relays] 100% CPU at random rate

[scullcactus]

Hello list.

This is my 1st message here, and I'm not a pro, so please excuse me if I
do something wrong.

I run a relay for several years now. This is my personal notebook so I
only start Tor when I power it up. I set it up for 2 things: to be a
node (non-exit) and to serve me as a SOCKS proxy for accessing some
sites I have here blocked.
My problem is, and long time has been, the following. Every 30-40-60-120
minutes (it varies) I suddenly see CPU consumption jumps to 100% because
of tor process, so I need to stop/start it to settle things down. Also,
when I start Tor after a period of inactivity, say, a few hours or
night, I cannot start it reliably for the first time, ever. It goes up
to "Bootstrapped 95% (circuit_create): Establishing a Tor circuit" log
message and... 100% CPU. After the second start, I get 100% CPU with
50/50 probability, and after the 3rd, it finally is OK, most of the
time. Then, this 30-40-60-120 minutes cycle begins... It happens with
this "Bootstrapped 95% ..." message or a bit  before that.
I experienced it with many 0.3.x, 0.4.1.x versions, now with 0.4.2.x
versions also. I tried not to restart tor process when it eats my CPU
for several minutes but it doesn't stop, so I have to stop/start it
manually.
I see nothing bad in the log at its NOTICE level.

My setup now is:
Windows 8
Tor is 0.4.2.6
Fingerprint BF4591C167FF01B8AAE2749CD9D04913BD6743C4
I run Tor as a Service (--service install cli option; start manually)
My notebook is decently powerful and so is my network connection

My torrc is basically like this:

SOCKSPort [port]
SOCKSPolicy accept private:*,reject *:*
Log notice file C:\tor-0.4.2.6\var\notice.log
DataDirectory C:\tor-0.4.2.6\var
ControlPort [port]
HashedControlPassword [cencored]
MaxMemInQueues 1 Gb
Address [my real ip]
Nickname skullcactus
ORPort 59001 NoListen
ORPort 192.168.0.84:9001 NoAdvertise
DirPort 59030 NoListen
DirPort 192.168.0.84:9030 NoAdvertise
RelayBandwidthRate 3 MBytes
RelayBandwidthBurst 6 MBytes
ExitRelay 0
GeoIPFile C:\tor-0.4.2.6\Data\Tor\geoip
GeoIPv6File C:\tor-0.4.2.6\Data\Tor\geoip6
ExcludeExitNodes [some exclusions]
StrictNodes 1
TrackHostExits [some hosts]
TrackHostExitsExpire 600
HeartbeatPeriod 1 hours

Really, I want to keep my node working but it gets on my nerves :-) .
Can you please help me track the problem down?