AWS MSSQL RDS Instance periodically timing out

Every 5 or so days (including just now) I get a barrage of timeout errors from my webapp.

If I look at what my SQL instance is doing in CloudWatch, it reports this:

Freeable space: http://cl.ly/NBRM

DB Connections: http://cl.ly/NBLH

Write throughput: http://cl.ly/NBFs

Read IOPS: http://cl.ly/NBp3

Write IOPS: http://cl.ly/NAre

Queue: http://cl.ly/NBA7

What the heck is happening? I don't believe its traffic related.How do I find out what happened?

**Update: ** incremental backups are taken every 5 mins, and daily backups are done at 4am (i.e. not when this happens)

Thanks