Obviously, if we want our communication to be effective, we have to be continually on our guard to detect such noise, whatever the source. When we find it, we must drown it out. Or better still, eliminate it altogether.

Of course, before we can overcome such barriers, from wherever they come, we must be able to recognize them. When they take the form of literal noise, they're usually easy enough to distinguish.

But what we don't appreciate enough is the plethora of forms of metaphorical noise. In the workplace, for example, we often find conflicting thoughts competing for attention.

Most business executives (and their secretaries!) are familiar with this type of scenario: the boss may call for a certain file from the filing cabinet, and be quite amazed that this simple request turns out to be so problematic.

He or she doesn't know this instruction has triggered an unexpected stimulus: ''File? Yes, I must remember to stop by the store on the way home to pick up a nail file...''

Then again, many executives fail to realize the extent to which distrust can distort messages. A manager who routinely insists that every printing order is urgent, is not too likely to find receptive ears when time really is of the essence.

Let's take a look at an incident in the working lives of two very special imaginary characters - Mr Thompson, Chief Operating Officer of a flourishing corporation, and his work supervisor, Mr Brown..

This is a day for which Mr Brown has been waiting in very keen anticipation. Why?

Our Mr Brown has been rather unhappy of late.

The economic downturn hasn't touched our company yet. Business, in fact, is booming. Mr Brown has no complaints about that, for he's a devoted worker, to say the least, and he's gratified to be a key player in his firm's success. He has never been one to panic at the prospect of hard work.

Then what's the problem? Simply this: relative to the time and energy he has invested in his job, Mr Brown is underpaid. Period.

But a few weeks ago, he took the bull by the horns.

Knocking on Mr Thompson's door, he explained that, in the long run, a hefty raise would be in the company's interest as much as his own. In return, moreover, he would be very happy to take on extra responsibilities.

Our COO seemed more than sympathetic. The vice president in charge of the budget was out of the country at that moment, but Mr Thompson promised to raise the matter immediately on the VP's return. In all probability, his consent would be a mere formality.

Today is the day that has been set down for the verdict to be delivered.

The butterflies in our supervisor's stomach give way to cautious optimism as he enters his superior's office. He has faith in the justice of his cause, and isn't Mr Thompson on his side?

''Ah, Mr Brown, good to see you!''

Mr Thompson's warm smile suddenly freezes in mid-air. His face seems to change color - or perhaps we're just imagining it?

''Ahem...Yes...'' He pauses for the proverbial two seconds that seem like an eternity. What's the matter? Has Mr Thompson, who never forgets anything, only just remembered something important?

''Look, I'm sorry, I didn't have a chance to discuss that matter with Mr Hodgkinson yet, but I have some important information in connection with our machinery problems. Can you make a note of a few things?''

But Mr Brown, the epitome of conscientiousness, is as human as the next person. He's hardly in a state for mental notes.

The kind of emotional blackout the work supervisor is now experiencing is an obstacle to effective communication as real as it's intangible.

It's no less of a barrier than the noise of a pneumatic drill punctuating the conversation of two people in the street.