High load average every 105 minutes

I have Postgresql 9.3 installed on AWS instance ubuntu 14.04

The load average of the instance increase every 105 minutes even without any database. I’ve checked the scheduled jobs but couldn’t find anything suspicious. When the load average was at peak, I couldn’t see any process consuming resources. This happens on all my servers that has postgresql installed, even after I purge postgresql. Has anyone seen this before?

Here’s my config:
postgresql.conf

data_directory = '/var/lib/postgresql/9.3/main'
hba_file = '/etc/postgresql/9.3/main/pg_hba.conf'
ident_file = '/etc/postgresql/9.3/main/pg_ident.conf'
external_pid_file = '/var/run/postgresql/9.3-main.pid'
listen_addresses = '*'
port = 5432
max_connections = 100
unix_socket_directories = '/var/run/postgresql'
ssl = true
ssl_cert_file = '/etc/ssl/certs/ssl-cert-snakeoil.pem'
ssl_key_file = '/etc/ssl/private/ssl-cert-snakeoil.key'
shared_buffers = 128MB
shared_preload_libraries = 'pg_stat_statements'
wal_level = hot_standby
checkpoint_segments = 8
max_wal_senders = 3
wal_keep_segments = 8
log_min_duration_statement = 300
log_line_prefix = '%m '
log_timezone = 'UTC'
datestyle = 'iso, mdy'
timezone = 'UTC'
lc_messages = 'en_US.UTF-8'
lc_monetary = 'en_US.UTF-8'
lc_numeric = 'en_US.UTF-8'
lc_time = 'en_US.UTF-8'
default_text_search_config = 'pg_catalog.english'

Nhan Nguyen
System Engineer

MB: (+84) 934 008 031
Skype: live:ducnhan813