Problem query overloading server

[dfc005]

OK,

Have just had word from our server manager who has told us that there is a query that is overloading the server at random intervals but happening regularly throughout the day.

I've try disabling all plugins and custom mods, using the default style and a few other tricks but it doesn't seem to be stopping the query.

I was hoping someone could indicate where this query is being initated from and then hopefully that would help me track done what's causing the overload.

SELECT
    userfield.*, usertextfield.*, user.*, UNIX_TIMESTAMP(passworddate) AS passworddate,
    IF(displaygroupid=0, user.usergroupid, displaygroupid) AS displaygroupid,
    language.phrasegroup_global AS phrasegroup_global,
    language.options AS lang_options,
    language.languagecode AS lang_code,
    language.charset AS lang_charset,
    language.locale AS lang_locale,
    language.imagesoverride AS lang_imagesoverride,
    language.dateoverride AS lang_dateoverride,
    language.timeoverride AS lang_timeoverride,
    language.registereddateoverride AS lang_registereddateoverride,
    language.calformat1override AS lang_calformat1override,
    language.calformat2override AS lang_calformat2override,
    language.logdateoverride AS lang_logdateoverride,
    language.decimalsep AS lang_decimalsep,
    language.thousandsep AS lang_thousandsep
FROM 
	user AS user
LEFT JOIN 
	userfield AS userfield ON (user.userid = userfield.userid)
LEFT JOIN 
	usertextfield AS usertextfield ON (usertextfield.userid = user.userid) 
LEFT JOIN 
	language AS language ON (language.languageid = IF(user.languageid = 0, 1, user.languageid))
WHERE 
	user.userid = 2282549

Some additional points are that our user database is very large with over one million registered users and we have quite a lot of traffic, approx. 150K users (combo of guest and registered) visiting per day.

Hoping someone can help me out here!